Hydrostatic spindle



Jan. 20, 1970 M. GREENBERG 3,490,819

HYDROSTATIC SPINDLE Filed Jan. 18, 1968 2 SheQbS-Shee'll 2 INVENTOR. MYRQN L. GREENMR@ ATTRNEYS Unite 3,490,819 HYDROSTATIC SPINDLE Myron L. Greenberg, Union Lake, Mich., assignor to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Jan. 18, 1968, Ser. No. 698,945 Int. Cl. B611 17/00; F16c 1/24 U.S. Cl. 308-122 13 Claims ABSTRACT F THE DISCLOSURE This invention relates to hydrostatic spindles. In the design and testing of hydrostatic spindles which have longitudinally spaced sets of pressure pads, it is common procedure to predict lateral moment stiffness of the spindle by approximately the following method:

1) The lateral load capacity of a `journal element is determined by a conventional approximation, usually that of projected area (journal dia=meter length of one pad) times an effective pressure which can ybe determined from pocket pressure and a geometric constant associated with the pad configuration. These procedures are well known and need no elaboration.

(2) The journal element forces are assumed to be acting at the center of the pads, and the moment arm is assumed to be the distance between centers.

(3) The moment stiffness is then the angular deflection divided into the product of load capacity of a journal element and moment arm.

Assuming that,

S=pad length (in.)

:moment arm (in.)

d=journal diameter (in.)

ap=pad efficiency coefficient (dimensionless) F=load capacity of one journal element (lb.) Pu=pocket pressure A=projected area of one journal element h=gap (in.)

Then:

M=moment capacity A=dS F=apdsPo M=Fl=apIdsPo x=possible angular deflection (radius) then:

tan azzand moment stiffness :gllg

(l-l-s) However, this is an instantaneous expression. If we assume that the compensation is linear up to 85% of full deflection, then the greatest possible value of P0'=.S5Pm,

States Pater and the maximum stiffness, which is the figure we are after, becomes:

53:@ in.lb./radian Z-l-s In a typical case, ap=.6 S24" d=2.5 l=8" Pm=300 p.s.i. h=.001"

This appears on the surface to be a simple and straightforward way of calculating, which should produce fairly accurate predictions of compliance. In fact, however, predictions made by this method vary from twice to five times too high. Although I do not wish to be 'bound by the theory involved, it is believed that at least two effects contribute to this regrettable situation; the nonlinearity of pocket pressure change with respect to deflection (assuming a rigid shaft), and deflection of the shaft, which introduces curvature about an axis perpendicular to the spindle axis and further increases this nonlinearity.

A hidden and infrequently noted assumption always made in the design of hydrostatic bearings of this type is that all of the above calculations, and all of the considerably more complex ones of which these are a working simplification are based on the assumption that the gap between shaft and housing is constant over the full extent of any given pad, especially those in the plane of the applied moment. In some situations this is a legitimate approximation, but in the case of a spindle I have determined that the gap can easily vary 30% along the open side and to an even greater degree on the short side. This situation produces, in place of the uniform flow and pressure gradient around a pad usually assumed, a very large variation in these parameters as the perimeter of the pad is traversed. Since flow is proportional to the' cube of the gap, the average flow will be much too high and will produce a much lower maximum pocket pressure than is predicted yby the simplified theory and so a much lower actual stiffness.

It is an object of this invention to overcome this diculty by providing a configuration rwhose stator-to-rotor gap becomes more uniform as the deflection increases, which can be manufactured with reasonable facility, and which has a higher moment stiffness at large deflections.

In the drawings:

FIG. 1 is a longitudinal sectional View through a rotary spindle embodying the invention.

FIG. 2 is a fragmentary sectional view taken along the line 2 2 in FIG. l.

FIG. 3 is a diagrammatic view of the spindle shown in FIG. 1 showing the action of the spindle under lateral load.

FIG. 4 is a partly diagrammatic longitudinal sectional view through a modified form of rotary spindle.

FIG. 5 is a partly diagrammatic part sectional view through a further modified form of rotary spindle.

Referring to FIG. l, a rotary spindle 10 embodying the invention comprises a housing 11 having a bore 12 in which a rotor 13 is positioned for rotation and axial movement relative to the housing. The rotor has a cylindrical outer surface 14. The housing has generally complementary annular surfaces 15 each of which has circumferentially spaced pressure pads or pockets 16 therein with associated restrictors 17, that may be in the form of capillary tubes, to which fluid under pressure is supplied through inlet line 18. An annular drain groove 19 is provided for collecting the fluid that flows inwardly from the pockets 16. External drains and seals, not shown, complete the system. The iluid flows from pocket 19 to a passage 20 and then to the reservoir. This configuration is not part of this invention and is shown in the patent to Porath 3,200,671.

In accordance with the invention, the annular surfaces 14, are so related that when the axis of the rotor 13 is aligned with the axis of the bore 12, the surfaces 14, 15 diverge axially and radially outwardly. As a result when the moment load is applied laterally on the rotor 13 as shown in FIG. 3, the surface 14 of the rotor is brought into substantially parallel relation to the surface 1S at the areas 15a, 15b resulting in considerably improved stiffness. As shown diagrammatically in IFIG. 3 wherein arrows represent the pressure pockets and restrictors, the tapering relation of the surfaces 14, 15 is exaggerated. In practice it is small being on the order of 0.0003" in 21/2" of axial length of the surface.

Although I do not wish to be bound by the theory involved, in my opinion, the increased stiffness is achieved by providing the relationship such that upon lateral load on the rotor the two complementary surfaces are brought into nearly parallel relation resulting in the more effective pressure compensation.

In the form of the invention shown in FIG. 4, (see Porath 3,223,463) the pressure pads and associated restrictors are shown in the form of arrows for purposes of clarity. In this form the surfaces 21 of the housing 22 are parallel to the axis of the bore in the housing and the complementary surfaces 23 of the rotor 24 are tapered to produce the tapering relationship of the surfaces 23, 21 when the axis of the rotor 24 is aligned with the axis of the bore in the housing. This is possible since in such a trapped spindle, there is no axial motion.

In addition radially extending flanges 25 are provided at longitudinally spaced points on the rotor 24 and are associated with surfaces 26 on the housing that have circumferentially spaced pressure pockets and restrictors 27. In this form the surfaces 28, 26 taper outwardly relative to one another when the axis of the rotor 24 and the bore in the housing are aligned so that when there is a lateral moment load on the rotor as shown in exaggerated position shown in FIG. 4, not only are the surfaces 23, 21 brought into more nearly parallel relation but in addition portions of the thrust surfaces 26, 28 are brought into more nearly parallel relation.

In the form of the invention shown in FIG. 5, the housing 30 has surfaces 31, 32 in which the pressure pockets and restrictors 33 are provided, as in the form of the invention shown in FIGS. l and 3, while the rotor 34 has a radial flange 35 with surfaces 36, 37 that are tapered with relation to radial surfaces 38 in the housing 30. Pressure pockets and associated restrictors 39 are provided in the surfaces 38. When the axis of the rotor 34 is aligned with the axis of the bore in the housing 30, the surface of the rotor and the surfaces 31, 32 diverge outwardly and radially while the surfaces 36, 38 and 37, 38 diverge outwardly.

It will be understood that some sacrifice in axial thrust load is made by tapering surfaces 36, 37. lf thrust capacity is more important than the comparatively minor additional moment capacity of the thrust surfaces, then the taper on surfaces 36, 37 can be omitted.

I claim:

1. In a hydrostatic spindle, the combination comprising a housing having a bore therein,

a rotor in said bore,

said bore and said rotor having two longitudinally spaced generally axially extending complementary surfaces,

each surface of one of said housing and said rotor having circumferentially spaced pressure pockets therein,

a restrictor associated with each said pressure pocket,

means for supplying uid under pressure to each said restrictor,

each surface of one of said bore and said rotor tapering axially and radially outwardly with respect to the complementary surface of the other of said bore and said rotor when the axis of the rotor and the axis of the bore are aligned whereby when uid is supplied to each of said pressure pockets and a lateral moment load is provided on said rotor and provides improved maximum level of uid pressure within the pressure pocket.

2. The combination set forth in claim 1 wherein said pressure pockets are provided on said housing.

3. The combination set forth in claim 1 wherein said surfaces of said housing are tapered outwardly and radially.

4. The combination set forth in claim 1 wherein said surfaces of said rotor are tapered.

5. The combination set forth in claim 1 including a pair of longitudinally spaced radially extending flanges on said rotor,

said housing having generally complementary radially extending surfaces,

one of said surfaces having a plurality of circumferentially spaced pressure pads thereon,

restrictors associated with said last-mentioned pressure pads,

and means for supplying uid under pressure to said last-mentioned restrictors,

the radial surfaces of said flanges and the radial surfaces of said housing normally diverging outwardly relative to one another when the axis of the bore and the axis of the rotor are aligned.

6. The combination set forth in claim 1 wherein said rotor has a radial flange thereon,

said flange having generally radial surfaces thereon,

said housing having generally complementary radial surfaces,

curcumferentially spaced pressure pockets on one of said surfaces,

a restrictor associated with each said pressure pocket,

and means for supplying lluid under pressure to said last-mentioned restrictors,

said radial surfaces of said flange and said radial surfaces of said housing being tapered outwardly relative to one another when the axis of said bore and the axis of said rotor are aligned.

7. In a hydrostatic spindle, the combination comprising a housing having a bore therein,

a rotor in said bore,

said bore and said rotor having two longitudinally spaced generally axially extending complementary surfaces,

each surface of one of said rotor and said bore being cylindrical,

each surface of said housing having circumferentially spaced pressure pockets therein,

a restrictor associated with each said pressure pocket,

means for supplying fluid under pressure to each said restrictor,

each surface of one of said bore and said rotor tapering axially and radially outwardly with respect to the complementary surface of the other of said bore and said rotor when the axes of said rotor and said bore are aligned whereby when iluid s supplied to each of said pressure pockets and a lateral moment load is provided on said rotor and provides improved maximum level of fluid pressure within the pressure pocket.

8. The combination set forth in claim 7 wherein said pressure pockets lare provided on said housing.

9. The combination set forth in claim 7 wherein said surfaces of said housing are tapered outwardly and radially.

10. The combination set forth in claim 7 wherein said surfaces of said rotor are tapered.

11. The combination set forth in claim 7 including a pair of longitudinally spaced radially extending flanges on said rotor,

said housing having generally complementary radially extending surfaces,

said radially extending surfaces of one of said rotor and housing forming a right angle with respect to the axes of said one of said rotor and said housing,

one of said surfaces having a plurality of circumferentially spaced pressure pads thereon,

restrictors associated with said pressure pads,

and means for supplying uid under pressure to said last-mentioned restrictors,

the radial surfaces of said flanges and the radial surfaces of said housing normally diverging outwardly relative to one another when the axis of the bore and the axis of the rotor are aligned.

12. The combination set forth in claim 7 wherein said rotor has a radial flange thereon,

said ange having generally radial surfaces thereon,

said housing having generally complementary radial surfaces,

a circumferentially spaced pressure pocket on said radial surfaces of said housing,

a restrictor associated with each said pressure pad,

and means for supplying fluid under pressure to said last-mentioned restrictor,

said radial surfaces of said flange and said radial surfaces of said housing being tapered outwardly relative to one another when the axis of said bore and the axis of said rotor are aligned.

13. The combination set forth in claim 7 wherein said rotor has a radial flange thereon,

said ange having generally radial surfaces thereon,

said housing having generally complementary radial surfaces,

a circumferentially spaced pressure pocket on said radial surfaces of said housing,

a restrictor associated with each said pressure pad,

and means for supplying fluid under pressure to said last-mentioned restrictor.

References Cited UNITED STATES PATENTS 3,193,334 7/1965 Porath 308-9 3,223,463 12/ 1965 Porath 308-9 3,200,671 8/1965 Porath 308-9 FOREIGN PATENTS 107,213 4/1927 Austria.

MARTIN P. SCHWADRON, Primary Examiner FRANK SUSKO, Assistant Examiner 

